1. Field of the Invention
The present invention relates to a battery pack wherein a nonaqueous electrolyte secondary battery capable of charge and discharge, or a lithium-ion secondary battery or the like in particular, to be used as the power supply mainly for a portable electronic device such as a video camera, a mobile computer or a mobile telephone is held in an insulating case.
2. Description of Related Art
In recent years, a nonaqueous electrolyte secondary battery, such as a lithium-ion secondary battery, which is capable of charge and discharge and has the shape of a rectangular parallelepiped is mainly used as the power supply for a portable electronic device, such as a video camera, a mobile computer or a mobile telephone, which is spreading rapidly.
A battery assembly is obtained by disposing a protection circuit substrate for controlling the voltage of a cell at one side face of a lithium-ion secondary battery (cell) in order to prevent overcharge and overdischarge. A battery pack obtained by housing the battery assembly in an insulating case, made of synthetic resin for example, is mounted in an electronic device. The protection circuit substrate and the cell are electrically connected with each other by a lead plate for connection.
Disclosed in Japanese Patent Application Laid-Open No. 2005-190852 is an invention of a battery pack assembled by holding a cell in an upper case and a lower case, which are prepared by splitting a case parallel to a flat surface portion of a battery assembly having the shape of a square flat plate into an upper part and a lower part and respectively have the shape of a box of one surface opening, and then joining the cases by a method such as ultrasonic welding.
FIG. 1 is an exploded perspective view showing the same battery pack as that of Japanese Patent Application Laid-Open No. 2005-190852, and denoted at 61 in the figure is a battery pack.
A cell 62a of a battery assembly 62 of the battery pack 61 is a nonaqueous electrolyte secondary battery, such as a lithium-ion secondary battery, having the shape of a square flat plate, which is made by holding electrode assembly having a positive electrode and a negative electrode wound via a separator and nonaqueous electrolyte in a case made of aluminum or aluminum alloy.
The battery assembly 62 is constructed by laying down a protection circuit substrate 62b on one end face of the cell 62a. The top face of the protection circuit substrate 62b is provided with protection circuits 62c and 62c for preventing overcharge, overdischarge or the like and is connected with a positive electrode plate and a negative electrode plate (not illustrated) to be electrically connected with the cell 62a. Output terminals 62d, 62d and 62d for taking out electric power to the outside as well as taking in electric power from the outside for charge are provided at the rear face of the protection circuit substrate 62b in a form of gold plating.
A lower case 63 of the case is made by disposing side plate portions 63b and 63b on the long side and side plate portions 63c and 63c on the short side on the circumference of a flat plate portion 63a. The flat plate portion 63a is provided with window portions 63d, 63d and 63d from which the output terminals 62d, 62d and 62d are exposed.
Side plate portions 64b and 64b on the long side and a side plate portion 64c on one short side are disposed on the circumference of a flat plate portion 64a of an upper case 64. Provided on the other short side of the upper case 64 in two tiers are: a side plate portion 64h; and a substrate covering portion 64d comprising an upper plate portion 64e and side plate portions 64f, 64g and 64g. 
The battery pack 61 is assembled by holding the battery assembly 62 in the lower case 63, then covering the assembly with the upper case 64 and joining the upper case 64 and the lower case 63 by ultrasonic welding.
Disclosed in Japanese Patent Application Laid-Open No. 2005-190956 is an invention of a battery pack constructed by assembling an upper case and a lower frame, which is made to have the shape of a window frame by providing an opening at a closed-end face of a case, and then wrapping a label around the assembly.
Disclosed in Japanese Patent Application Laid-Open No. 2005-100689 is an invention of a battery pack constructed by assembling an upper frame and a lower frame, which are respectively made to have the shape of a frame by providing an opening at a closed-end face of an upper case and a lower case, and then wrapping a label around the assembly.
FIG. 2 is an exploded perspective view showing the same battery pack as that of Japanese Patent Application Laid-Open No. 2005-100689, and denoted at 71 in the figure is a battery pack.
A battery assembly 72 is constructed by laying down a protection circuit substrate 72b on one end face of a cell 72a. The top face of the protection circuit substrate 72b is provided with protection circuits 72c and 72c for preventing overcharge, overdischarge or the like and is connected with a positive electrode plate and a negative electrode plate (not illustrated) to be electrically connected with the cell 72a. Output terminals 72d, 72d and 72d are provided at the rear face of the protection circuit substrate 72b in a form of gold planting.
A lower frame 73 of the outer frame is made by disposing side plate portions 73b and 73b on the long side and a side plate portion 73c on one short side on the circumference of a bottom plate portion 73a having the shape of a window frame. Provided on the other short side of the lower frame 73 is a substrate placing portion 73d comprising a bottom plate portion 73e and side plate portions 73f, 73g and 73g. The bottom plate portion 73e is provided with window portions 73h, 73h and 73h from which the output terminals 72d, 72d and 72d are exposed.
An upper frame 74 is made by disposing side plate portions 74b and 74b on the long side and a side plate portion 74c on one short side on the circumference of an upper plate portion 74a having the shape of a window frame. Provided on the other short side of the upper frame 74 in two tiers are: a side plate portion 74h; and a substrate covering portion 74d comprising an upper plate portion 74e and side plate portions 74f, 74g and 74g. 
The battery pack 71 is assembled by holding the battery assembly 72 in the lower frame 73, then covering the assembly with the upper frame 74 and joining the upper frame 74 and the lower frame 73 by ultrasonic welding.
A label 75 is then wrapped to cover both of the exposed faces of the battery assembly 72, the side plate portions 74b and 74b of the upper frame 73 and the side plate portions 73b and 73b of the lower frame 73. The label 75 is doubly wrapped at the rear face side of the battery assembly 72.
Disclosed in Japanese Patent Application Laid-Open No. 2005-135770 is an invention of a battery pack constructed by fitting a right frame and a left frame, which are U-shaped by splitting an outer frame for covering side faces of a battery assembly in a direction perpendicular to a flat surface of the battery assembly into a right part and a left part, to the battery assembly and then wrapping a label around the assembly.
Disclosed in Japanese Patent Application Laid-Open Nos. 2004-327378 and 2005-158452 are inventions of battery packs constructed by uniting an upper frame and a lower frame of an outer frame, which have the shape of a window frame, to cover side faces of a battery assembly or uniting a right frame and a left frame of an outer frame, which are U-shaped, to cover side faces of a battery assembly, and then wrapping a label around the assembly.
Disclosed in Japanese Patent Application Laid-Open No. 2003-229105 is an invention of a battery pack constructed by forming a connection circuit peripheral portion by insert molding with low-temperature molding resin and then attaching or wrapping a label, without using a case.
Disclosed in Japanese Patent Application Laid-Open No. 2006-164559 is an invention of a battery pack comprising a case made by: forming a rectangular frame member surrounding the outer periphery of a battery assembly which is provided with a protection circuit substrate at one end face of a cell, in an integrated manner with a rectangular plate for covering a lower face of the battery assembly to make a frame member at one end face side to be a connecting frame from which output terminals are exposed; and providing a fitting portion into which the protection circuit substrate is fitted, at the connecting frame.
With the battery packs in Japanese Patent Application Laid-Open Nos. 2005-190852, 2005-190956, 2005-100689 and 2005-135770 wherein two cases or outer frames are assembled, there is a problem that the accuracy of dimension of a battery pack is the cumulative amount of the accuracy of dimension of the respective cases or outer frames and enhancement of the accuracy of dimension has a limitation. Moreover, assembling of a battery pack is cumbersome. Furthermore, methods for assembling two cases or outer frames, such as ultrasonic welding, adhesion and fitting using a locking claw, respectively have the following problems.
Ultrasonic welding has a drawback that expensive facilities and special jigs are required and the initial cost for starting commercial production is high. There is also a problem that it is necessary to provide predetermined clearance between a flat plate side of an upper case and a battery assembly so that the ultrasonic energy is not applied directly to a cell and electronic components on a connection circuit since direct application of ultrasonic energy sometimes damage components, and thickness reduction of a battery pack has a limitation.
Adhesion using instant adhesive has a drawback that whitening by the action of desiccant added to adhesive causes a defective appearance. Adhesion using other adhesive has a drawback that hardening takes time and much man-hour is required. There is also a problem that adhesive is likely to get out of adhesive surface, causing a defective appearance.
Fitting using a locking claw has a problem that it is difficult to strengthen fitting so as to prevent breakup at the time of fall or disassembly by a user. Accordingly, fitting using a locking claw is not used alone for assembling but is used mainly as auxiliary fitting to be used before label attachment for a battery pack of a label wrapping type.
With battery packs in Japanese Patent Application Laid-Open Nos. 2005-190956, 2005-100689, 2005-135770, 2004-327378, 2005-158452 and 2003-229105 which are constructed by wrapping a label on whole circumference of a battery assembly, it is necessary to provide a double or triple superposition portion at the end sides of a label in order to prevent the surface of the battery assembly from being exposed to the outside. When the superposition portion is provided, there is a problem that a step is generated around the superposition portion, degrading the appearance of the battery pack.
In the invention in Japanese Patent Application Laid-Open No. 2006-164559 wherein a battery assembly is fitted into a case formed in an integrated manner to have the shape of a box, it is possible to retain output terminals of the battery assembly at fixed positions of the case simply and easily.
The technical advance of thickness reduction has made it possible to realize a cell having a thickness of approximately 3 mm, and it is contemplated that thickness reduction of a battery pack further progresses by using such a cell. For this purpose, it is necessary to reduce the thickness of the entire battery assembly provided with a protection circuit substrate. When the thickness of a cell is reduced as described above, however, there is a problem that the vertical dimension of a protection circuit substrate, which is stood at a side face of the cell, becomes too short and it becomes impossible to mount IC, FET and various kinds of electronic components constituting the protection circuit and to provide output terminals. That is, a battery pack wherein a protection circuit substrate is stood has a problem that thickness reduction has a limitation and the invention in Japanese Patent Application Laid-Open No. 2006-164559, which is a battery pack wherein a protection circuit substrate is stood, has a limitation in thickness reduction.